Optical tracking markers may be used with cameras in a motion capture system to track and analyze the movement of a subject. This technology has been used to study biomechanics and physical capabilities of human and animal subjects in physical therapy and performance assessments. The technology has also been used in animation to achieve more lifelike and natural poses and movements for products like movies and video games.
For use in a motion capture system, optical tracking markers, which are often, for example, polystyrene spheres, are placed on a subject at particular locations which will best indicate how the subject is moving and the relationships between markers of particular interest. The optical tracking markers are coated with a retro-reflective material which enhances the amount of light reflected back from the surfaces of the markers. The cameras, which are often infrared cameras, for example, are calibrated to record only light with a certain threshold of brightness. The cameras then record only the markers because of the enhanced reflection of light from their surfaces relative to other surfaces in the recorded field. The recorded positions of the markers can then be used as a frame and can either be analyzed to assess biomechanics and physical capabilities or can be modified and animated to create realistic animation based on natural movements.
For the optical tracking markers to accurately indicate the movement and relationships of particular locations on the subject's body, it is important that they are properly and securely affixed to the subject. If the marker is loose, the recorded movement will include artifacts of the marker bouncing and moving separately from the subject. Known methods of affixing the markers to the subject include attaching the marker directly to the subject, removably attaching the marker to an article of clothing that the subject wears or permanently integrating the marker into an article of clothing that the subject wears. Each method of attaching markers to the subject creates specific challenges and disadvantages.
Markers that are attached directly to the subject must be affixed firmly enough to eliminate unwanted movement, but must also be easily and painlessly removed from the subject's body following the data collection. Double sided tape and medical tape are normally used to attach markers directly to the subject. In order for the markers to be successfully attached to the subject, the double sided or medical tape must be sufficiently sticky and must be able to maintain stickiness while the subject is in motion for the duration of the data collection. If the tape is too sticky, however, it may be difficult or painful to remove the markers from the subject. Additionally, a subject's skin may be irritated or react allergically to the adhesive in the tape. It is desirable to attach the markers to the subjects in a way that will overcome the challenges presented by using double sided or medical tape to attach markers directly to the skin of subjects.
Markers that are permanently integrated into clothing that the subject wears are firmly affixed to the article, but the article of clothing must also closely adhere to the subject. The article must fit the subject so that the markers align with the proper locations on the subject's body to record the desired movements and inter-body relationships. Markers that are permanently integrated into the article of clothing that the subject wears are often sewn on, woven in or snapped on to the material. If the article is too large for the subject, it will fit loosely and unwanted movements of the markers will be recorded. If the article is too small for the subject, the markers may not line up with the appropriate points on the subject's body. It is desirable to attach the markers to the subjects in a way that will overcome the challenges presented by markers that are sewn, woven or snapped on.
Markers that are removably attached to clothing that the subject wears must be affixed firmly to the article of clothing and the article of clothing must closely adhere to the subject in order to avoid unwanted movement of the marker. These markers must also be easily removed without damaging the subject's clothing. Hook and loop fasteners, double sided tape and adjustable straps are normally used to attach markers to an article of clothing that the subject wears. Limitations of attaching markers to clothing are two-fold. The hook and loop fastener, double sided tape or adjustable strap must be affixed firmly to the subject's clothing to avoid recording unwanted movement artifacts that result from the marker moving on the clothing. Concurrently, the subject's clothing must closely adhere to the subject to avoid recording unwanted movement artifacts that result from the clothing moving on the subject. It is desirable to attach the markers to the subjects in a way that will overcome the challenges presented by markers that are affixed to clothing that the subject wears with hook and loop fasteners, double sided tape and adjustable straps.
In view of the foregoing, it would be desirable to provide an improved marker attachment. Because the data recorded by a motion capture system are used for very detailed analyses of subtle differences and fine movements, the precision and accuracy of the marker movements are of utmost importance. It is desirable then that the improved marker attachment provides a quick and simple way to attach markers to subjects that addresses both properly positioning the markers on the subjects and firmly affixing the markers in those positions.